1. Field of the Invention
The present invention is directed to an apparatus for the implementation of a physiologically controlled measurement at a living subject.
2. Description of the Prior Art
In a number of examinations of living subjects, meaningful and diagnostically relevant measurements are possible only at specific points in time or during specific phases within a physiological cycle. In computer-tomographic examinations of internal organs that, for example, move in the rhythm of the heart beat or respiration, it can be easily understandable that only slice projections that were acquired during comparable phases of the organ movement can be meaningfully compiled to form a tomography image that is capable of being interpreted. Such measurements therefore are temporally controlled according to a suitably selected physiological signal. One or more relative points in time that are utilized for the time-control of the measurement are thereby defined on the basis of the physiological signal.
Methods referred to as triggered methods are known for defining these relative points in time. In these methods, a trigger pulse in the physiological signal is employed as a reference time. The relative points in time are then defined in temporal reference to this trigger pulse. Their definition ensues, for example, by indicating a waiting time (delay time) after every trigger pulse and by defining the length of an actual measurement time window (scan acquisition window) that begins after the delay time has passed and within which the measured data are to be registered. The parameters of xe2x80x9cdelay timexe2x80x9d and xe2x80x9cscan acquisition windowxe2x80x9d are usually entered in numerical form as input by the user via a keyboard. The scan acquisition window is derived from a number of other parameters that the user can set, for instance on the basis of a number of sub-measurements that are to be implemented per scan acquisition window. The length of the scan acquisition window then is derived from a multiplication of this number of sub-measurements by the time duration (repetition time) that is to be expended for every sub-measurement and which can likewise may be potentially set.
Further, there are methods referred to as gating methods. In these, a time window (gate) controlling the measurement is usually defined by amplitude thresholds of the physiological signal. When the physiological signal passes through such a threshold, then this is considered as a switch-on or switch-off time of the time window. Given a breathing-controlled measuring method, for example, a suitable percentage of the respiratory motion can be selected as threshold.
A problem associated with physiologically controlled measurements is that the signal parameters of the physiological signal employed as reference are often not constant but instead can be subject to considerable fluctuations. In particular, the signal parameters, for instance the signal cycle or the maximum or the average signal amplitude, can change between one phase of the measurement preparation and the phase of the actual measurement implementation, due, for example, to an increase of the heartbeat or respiration rate. When suitable values for the aforementioned parameters of waiting time, length of the scan acquisition window, threshold height and the like have been set in the preparatory phase, these parameter values may no longer be suitable in the following implementation phase of the measurement, and lead to measurement results that have little diagnostic utility.
It is an object of the present invention to provide a simple arrangement for reliably monitoring whether the (at least one) relative point in time to be employed for the time control of the measurement is still suitablexe2x80x94as soon as it has been set and compared to the current curve of the physiological signalxe2x80x94in order to be able to meaningfully implement the measurement.
This object is achieved in accordance with the invention in an apparatus for the implementation of a physiologically controlled measurement in a living subject, having a signal acquisition arrangement for acquiring a physiological signal of the subject, display for the graphic display of a time curve of the physiological signal, and a time-setting unit which sets at least one relative point in time that is referenced to the time curve of the physiological signal and that is to be employed for the control of the time sequence of the measurement.
In accordance with the invention the display is configured for also graphically displaying the at least one relative point in time in its temporal relationship to the physiological signal.
Due to the simultaneous, graphic display of the at least one relative point in time, the invention makes it possible for the user to continuously visually check whether the respective relative point in time has been suitably set or must be adapted, by comparing the displayed relative point in time to the displayed, current signal curve of the physiological signal. This is possible at first glance because the relative point in time is displayed in temporal relationship to the physiological signal, i.e. based on the same time scale. A mere numerical value for the relative point in time is thus not merely mixed in the displayed information on the screen; rather, the time position of the relative point in time relative to the physiological signal is shown.
In a preferred embodiment of the invention, at least two different relative points in time can be set with the time-setting arrangement, with the display being configured for graphically displaying a time window lying between two relative points in time in temporal relationship to the physiological signal. Further, the display can be configured for graphically displaying a time window lying between a relative point in time and a reference point in time of the physiological signal in its temporal relationship to the physiological signal. The time windows can be especially easily visually recognized in an embodiment wherein they are displayed in the form of a time bar. In the case of a number of simultaneously displayed time windows, for example, different colors for the time bars can be employed.
It can be desirable in some instances for the display to display the physiological signal and the at least one relative point in time with a stationary time axis. In other instances, however, it is also desirable that the display to display the physiological signal and the at least one relative point in time with a moving time axis.